Device and method for tempering at least one process good

ABSTRACT

A method and for heat-treating at least one material being processed ( 3 ) under a specific process-gas atmosphere ( 111 ) of at least one process gas ( 4 ) with the aid of a heat-treatment unit ( 6 ). The heat-treatment unit has at least one energy source ( 5 ) for making the material being processed ( 3 ) take up an amount of energy, a heat-treatment container ( 11 ) with a heat-treatment space ( 16 ) for keeping the material being processed ( 3 ) under the process-gas atmosphere ( 111 ) during the heat treatment, a heat-treatment chamber ( 13 ), in which the heat-treatment container ( 11 ) is arranged at a distance ( 18 ) from the heat-treatment chamber ( 13 ), so that there is an intermediate space ( 14 ) between the heat-treatment container ( 11 ) and the heat-treatment chamber ( 13 ), and an element ( 19, 191 ) for producing in the intermediate space ( 14 ) a further gas atmosphere ( 141 ) of a further gas, different from the process-gas atmosphere ( 111 ).

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for heat-treating at least onematerial being processed in a heat-treatment space of a heat-treatmentcontainer under a specific process-gas atmosphere of at least oneprocess gas. An apparatus of this type is known for example from EP 0662 247 B1. In addition to the apparatus, a method for heat-treating amaterial being processed is presented.

The material being processed known from EP 0 662 247 B1 is amultilayered element which is produced by applying a functional layer toa supporting layer (substrate). In order that the functional layerand/or the supporting layer have a desired physical (electrical,mechanical, etc.) and/or chemical property, processing of the materialbeing processed or the layer and/or the supporting layer will be carriedout. The processing comprises heat-treating the material being processedin the presence of a gas (process gas).

For the heat treatment, the material being processed is arranged in aclosed heat-treatment container made of graphite. During the heattreatment, the material being processed is exposed to a process gas withgaseous selenium. During the heat treatment, the material beingprocessed takes up an amount of energy, with a partial amount of theamount of energy being supplied to each layer. The heat treatment takesplace, for example, at a heating-up rate of 10° C./s. A halogen lamp isused as the energy source of the amount of energy. With the halogenlamp, the heat-treatment container made of graphite is irradiated withan electromagnetic radiation, and consequently the heat-treatmentcontainer is heated up. Graphite has a high absorptivity for theelectromagnetic radiation in the spectral range of the halogen lamp. Theamount of energy absorbed by the graphite is supplied to the materialbeing processed by heat radiation and/or heat conduction. Theheat-treatment container consequently acts as a secondary energy sourceor as an energy transmitter.

Graphite has a high emissivity and a high thermal conductivity. When thematerial being processed lies on a base of the heat-treatment container,on an underside of the material being processed the amount of energy issupplied substantially by heat conduction. An upper side of the materialbeing processed is supplied with an amount of energy by heat radiation,heat conduction and convection.

The larger the material being processed (the larger the surface areathereof), the more varied the materials used in the material beingprocessed (for example greatly differing coefficient of thermalexpansion, different absorptivity for the amount of energy etc.) and thehigher a heat-treatment rate (heating-up rate, cooling-down rate), themore difficult it is to control a temperature homogeneity or temperatureinhomogeneity in the material being processed. The temperatureinhomogeneity may lead to mechanical stress in the material beingprocessed, and consequently to destruction of the material beingprocessed.

SUMMARY AND DESCRIPTION OF THE INVENTION

A problem which arises from the cited prior art is use of, or occurrenceof, toxic and/or corrosive gases in heat treatment (for example H₂Se).

The object of the invention is to demonstrate how safe and reliable heattreatment can be carried out even in the presence of toxic and/orcorrosive gases.

To achieve the object, an apparatus is specified for heat-treating atleast one material being processed under a specific process-gasatmosphere of at least one process gas with the aid of a heat-treatmentunit. The heat-treatment unit has at least one energy source for makingthe material being processed take up an amount of energy, aheat-treatment container with a heat-treatment space for keeping thematerial being processed under the process-gas atmosphere during theheat treatment, a heat-treatment chamber, in which the heat-treatmentcontainer is arranged at a distance from the heat-treatment chamber, sothat there is an intermediate space between the heat-treatment containerand the heat-treatment chamber, and a means for producing in theintermediate space a further gas atmosphere of a further gas, differentfrom the process-gas atmosphere. The further gas atmosphere in this casehas a pressure gradient.

The further gas atmosphere (which can be set) is distinguished, forexample, by a defined partial pressure of a gas or gas mixture (forexample air). It is also conceivable for the gas atmosphere to be avacuum. The intermediate space helps to avoid process gas from beingdischarged into the surrounding area (atmosphere). For this purpose, ina special configuration, the intermediate space encloses theheat-treatment space.

The means for producing the further gas atmosphere is, for example, agas cylinder, which is in connection with the intermediate space via oneor more openings. A vacuum pump is also conceivable. With both means, apressure gradient can be established in the intermediate space.

In a special configuration, the heat-treatment space and theintermediate space are connected to each other in such a way that apressure gradient can be set between the heat-treatment space and theintermediate space.

In a further configuration of the invention, there is at least oneheat-treatment unit, with an energy source for making the material beingprocessed take up an amount of energy. The energy source is, forexample, a flat bank of heaters, which is formed by a heater array. Theheater array comprises, for example, bar-shaped halogen lamps or heatingbars arranged parallel to one another. Each halogen lamp may in thiscase be arranged in a shroud for protection from exposure to the(corrosive) process gas or for easy assembly and disassembly. An energysource of this type sends electromagnetic radiation, in particular inthe form of infrared radiation (thermal radiation, intensity maximum ata wavelength between 1 μm and 2 μm). An energy source in the form of aresistance heating element, which emits thermal radiation, is alsoconceivable. An element of this type has, for example, graphite, siliconcarbide and/or a metal alloy such as nickel chromium. Additionallyconceivable is any electromagnetic radiation (microwaves, UV light)which can lead to a heating-up of the material being processed. Inaddition, heat conduction and convection are also conceivable for theheat treatment. In a further configuration of the invention, theheat-treatment unit has at least one means for cooling the materialbeing processed. This is accompanied by the advantage that a processsequence comprising various method stages, with at least one heating-upphase and cooling-down phase, can be carried out with the aid of thesame apparatus. The means for cooling is, in particular, a cooling gasand/or a cooling liquid. The cooling takes place with the aid of thecooling gas by convection, with, for example, a cooling gas that iscooler in comparison with the material being processed being directedpast the material being processed. The cooling may also take place byheat conduction, with the material being processed being in contact witha cooling element with a corresponding coefficient of thermalconductivity. It is conceivable for the cooling element to be anenclosure of the heat-treatment unit with a hollow space through whichthe cooling gas or the cooling liquid can be directed. In a furtherconfiguration, at least one of the energy sources is arranged in ashroud which is at least partially transparent to the electromagneticradiation of the energy source. For example, the shroud consists ofquartz glass. The shroud is preferably vacuum-tight. With the aid of theshroud, the energy source can be protected from contact with a processgas. Moreover, the shroud can be flowed through by a coolant, toaccelerate cooling down of the energy source and consequently of thematerial being processed. A further advantage of this configuration isthat the energy source can be easily exchanged.

In a special configuration, the shroud of the energy source has anoptical filter for the electromagnetic radiation of the energy source.In this way, the optical property (absorptivity and transmissivity) ofthe shroud can be influenced in a specifically selective way.

In a special configuration, at least one of the heat-treatment units hasat least one transparent element, which has a specific absorption and aspecific transmission for at least one of the electromagnetic radiationsand which is arranged in the radiation field of the electromagneticradiation between the energy source of the electromagnetic radiation andone of the materials being processed. The special advantage of thetransparent element, in particular when heat-treating a multilayeredelement, is presented further below in connection with the configurationof the heat-treatment unit.

In a special configuration, the shroud of the energy source, theheat-treatment container, the heat-treatment chamber, the transparentelement and/or a reflective element have a material which is inert withrespect to the gas. In particular, the material is selected from thegroup comprising glass, quartz glass, fused quartz, ceramic, glassceramic and/or metal. These materials are inert, i.e. unreactive, withrespect to a large number of process gases. Moreover, some materials,such as quartz glass or glass ceramic, have a low coefficient of thermalexpansion. This is particularly important in the case of an apparatuswhich is made up of component parts of various materials. Within apermissible tolerance, one dimension of a component part can change.This ensures that the apparatus is not destroyed during the heattreatment on account of mechanical stress, i.e. is preserved. What ismore, it makes it more easily possible to keep a check on a gasatmosphere. A possible gap of a component part or between the componentparts of the apparatus scarcely changes during the heat treatment as aresult of the low coefficient of thermal expansion of its componentparts. An additional advantage results from use of a machinable material(for example machinable ceramic, glass ceramic or machinable fusedquartz).

It is described below how it is ensured by various configurations of theheat-treatment unit that materials being processed of a large surfacearea, in particular multilayer bodies with an unsymmetrical sequence oflayers, can be heat-treated while controlling a temperature homogeneityof the material being processed.

The material being processed of the heat-treatment unit is, for example,a multilayered element which has a first layer and at least one secondlayer. The heat treatment takes place by an amount of energy being takenup by the multilayered element, with a first partial amount of theamount of energy being taken up by the first layer and a second partialamount of the amount of energy being taken up by the second layer. Theheat-treatment unit, which has at least one energy source of the amountof energy, is characterized in that the first layer is arranged betweena first energy source and the second layer and the second layer isarranged between a second energy source and the first layer. At leastone of the energy sources has an emission of a specific electromagneticradiation with a radiation field, and at least one of the layers has aspecific absorption for this electromagnetic radiation and is arrangedin the radiation field. In addition, at least one transparent element,which has a specific transmission and a specific absorption for theelectromagnetic radiation, is arranged in the radiation field betweenthe energy source with the radiation field and the layer which has theabsorption of the electromagnetic radiation and is arranged in theradiation field.

The transparent element helps to heat up the layers of the multilayeredelement individually, i.e. to control, regulate and/or preset in aspecifically selective way the partial amount of the amount of energywhich the layer takes up. For example, an amount of energy is determinedduring the heat treatment with the aid of a control loop (see below). Itis also conceivable for a presetting of the energy sources (for exampleenergy density, type of energy, etc.) to be sufficient without anadditional control loop. Individual heating-up of the layers of themultilayered element is possible even in the case of very highheating-up rates of from 1° C./s to, for example, 100° C./s and more.The individual heating-up succeeds in keeping a mechanical stresses anda deformation of the multilayered element thereby caused under certaincircumstances as small as possible during the heat treatment.

The basis for this is the transparent element, which is opticallypartially transmitting (semitransparent). The transmission, which for aspecific wavelength lies between 0.1 and 0.9, for example, allows theelectromagnetic radiation described above to pass through thetransparent element onto a layer. The layer can take up a correspondingamount of energy or partial amount of the amount of energy which isdirectly emitted by the energy source. The transparent element also hasa certain absorption for the electromagnetic radiation. The energy whichis thereby taken up may be emitted to a surrounding area in the form ofheat radiation and/or heat conduction. In a special configuration, theapparatus for heat-treating a multilayered element has a transparentelement which radiates and/or conducts heat in the direction of themultilayered element through the absorption of the electromagneticradiation. In this way it is possible to heat-treat a layer by heatradiation and/or heat conduction.

It is also conceivable for a first layer of the multilayered element,which transmits the heat radiation, to be heat-treated substantiallyonly by heat conduction, while a second layer of the same multilayeredelement is heat-treated substantially by the heat radiation from thesame transparent element. A first layer with a correspondingtransmission is, for example, a layer of glass. If electromagneticradiation of an energy source and/or a transparent element comes intocontact with the glass element, a small proportion of the radiation(approximately 4%) is reflected. Most of the radiation (>90%) passesthrough the glass more or less unhindered and then impinges on a secondlayer of the multilayered element. This radiation can be absorbed thereand leads to an amount of energy being taken up by the second layer. Theglass layer cannot be heat-treated sufficiently quickly by radiation orheat radiation at a very high heating-up rate. By contrast, relativelyquick heat treatment can be achieved by heat conduction if thetransparent element is able to take up a partial amount of the amount ofenergy and transmit it to the glass layer.

The case in which the transparent element itself is a layer of themultilayered element is also conceivable. The transparent element cantake up a partial amount of the amount of energy through absorption ofpart of the electromagnetic radiation and can pass on a further partialamount of the amount of energy by transmission, for take-up by a furtherlayer.

In a special configuration of the heat-treatment unit, one layer of themultilayered element is a supporting layer for at least one furtherlayer of the multilayered element. The multilayered element has, inparticular, an unsymmetrical sequence of layers. For example, themultilayered element comprises a supporting layer which is coated on oneside. Individual layers of the multilayered element may also be arrangednext to one another.

In a special configuration, one layer of the multilayered element has amaterial which is selected from the group comprising glass, glassceramic, ceramic, metal and/or plastic. Temperature-resistant plastic,such as Teflon, comes into consideration in particular as the plastic.One layer is, for example, a metal foil. The metal foil may also act asa supporting layer.

The partial amount of the amount of energy which is taken up by a layerdepends, for example, on the absorptivity, emissivity and/orreflectivity of the layer. It also depends, however, on the type ofenergy source and on the way in which the amount of energy istransmitted to the multilayered element or to a layer of themultilayered element.

One of the energy sources of the heat-treatment unit is, for example, anenergy source of thermal energy. The layer may be supplied with thethermal energy directly. Heat radiation, heat conduction and/orconvection come into consideration here. In the case of heat radiation,the energy source may itself be a source of heat radiation. The heatradiation is, for example, electromagnetic radiation in the wavelengthrange between 0.7 and 4.5 μm. The corresponding layer is arranged in theradiation field of the energy source. The layer is impinged by theelectromagnetic radiation of the energy source and at least partiallyabsorbs the electromagnetic radiation.

It is also possible, however, for a layer to be supplied with anydesired energy, which is converted into thermal energy in the layer. Forexample, a layer is irradiated with high-energy UV light, which thelayer absorbs. Absorption of a high-energy light quantum causes amolecule of the layer or the entire layer to become electronicallyexcited. Energy which is thereby taken up can be converted into thermalenergy.

In addition to heat radiation and heat conduction, it is also possiblefor a layer or the entire element to be heat-treated by convection. Inthis case, a gas with a specific energy is directed past the layer, withthe gas releasing the energy to the layer. Gas directed past may at thesame time act as process gas.

Moreover, a layer can also be cooled by heat conduction and/orconvection. In this case, negative thermal energy is supplied to thelayer. In this way, it is also possible to control the amounts of energyor the partial amounts of the amounts of energy and, for example,additionally influence the mechanical stresses in the multilayeredelement.

In a special configuration, there is an energy transmitter for thetransmission of the amount of energy to the multilayered element. Theenergy transmitter acts as a secondary energy source. The energytransmitter absorbs, for example, electromagnetic radiation of a primaryenergy source, for example a halogen lamp, from a higher energy band andconverts this electromagnetic radiation into heat radiation, which isabsorbed by the layer. The indirect and/or direct surronding area of themultilayered element may act as the energy transmitter during the heattreatment. It is conceivable for an energy transmitter to be arrangedwith the multilayered element for heat treatment in an interior space ofa heat-treatment container. The energy transmitter may also be arrangedoutside the container, for example on a wall of the heat-treatmentcontainer or at a distance from the heat-treatment container. It isconceivable for the energy transmitter to be a coating of theheat-treatment container. The energy transmitter is, for example, agraphite film. It is even possible for the heat-treatment containeritself to assume the function of an energy transmitter. A function ofthis type is provided, for example, in the case of a heat-treatmentcontainer made of graphite. Finally, the transparent element is nothingother than an energy transmitter. Similarly, in the case of energytransmission by convection, a gas acts as an energy transmitter.

An amount of energy which is taken up by the multilayered element maydiffer not only from layer to layer but also within a layer. Forexample, during the heat treatment, an edge effect occurs in themultilayered element or in a layer of a multilayered element. An edgeregion of the layer is at a different temperature than an inner regionof the layer. A lateral temperature gradient is established during theheat treatment. This takes place, for example, whenever a radiationfield of the energy source is inhomogeneous. In this case, an energydensity of the radiation field on a surface area to which the radiationis radiated is not identical everywhere. A lateral temperatureinhomogeneity may also be established when the radiation field ishomogeneous, if a greater amount of energy per unit volume is absorbedon account of the larger absorbing area per unit volume. To compensatefor the temperature gradient, it is possible, for example, to use anenergy source which comprises a multiplicity of subunits. Each subunitmay be actuated separately, and in this way each amount of energysupplied from a subunit to a layer can be set separately. An example ofan energy source of this type is an array or matrix of individualheating elements. An example of a heating element is a halogen lamp. Thearray or matrix can also be used to establish a lateral temperaturegradient in the layer. In this way, it would be possible, for example,to produce permanent or transient deformation of the layered element ina specifically selective way. An array or matrix is of great advantagein particular for the heat treatment of a multilayered element in whichlayers lie next to one another.

With respect to the energy source, it is advantageous if the energysource or the energy sources operate in a continuous mode. It is alsoconceivable, however, for the energy sources to make the amount ofenergy or the partial amounts of the amount of energy available to thelayers in a cyclical and/or pulsed mode. An energy source of this typeis, for example, an energy source with pulsed electromagnetic radiation.In this way, an amount of energy can be supplied to the layers at thesame time or within a temporal sequence (for example alternately).

The following properties of the energy source of electromagneticradiation are particularly advantageous:

The energy source has a homogeneous radiation field.

A spectral intensity distribution of the energy source partiallyoverlaps a spectral absorption of the layer, of the transparent elementand/or of any heat-treatment container that may be present (see below).

The energy source is corrosion-resistant and/or corrosion-protected inthe presence of a process gas.

The energy source has a high energy density, which is sufficient toallow a mass of the multilayered element (and, if appropriate, that of aheat-treatment container) to be heated up at a heating-up rate of over1° C./s.

In a special configuration, the transparent element of the apparatus hasat least one spacer, against which the multilayered element bears inorder for a laterally homogeneous amount of energy to be taken up by themultilayered element. For example, the layer by means of which themultilayered element rests on the transparent element or the spacer isprimarily heat-treated by homogeneous heat radiation. In this form, thespacer preferably has a material which has a low absorption for theelectromagnetic radiation. A spacer projects, for example, beyond asurface of the transparent element by a few μm to mm.

The layer resting on the spacers may also be primarily heat-treated byheat conduction. For this purpose, the spacers have, for example, athermal conductivity which is necessary to achieve a correspondingheat-treatment rate. For energy transmission by heat conduction, it isalso conceivable for the spacer to have a high absorption for anelectromagnetic radiation of an energy source, with the electromagneticradiation being additionally converted into thermal energy.

In particular, the transparent element has a multiplicity of spacers.With a multiplicity of spacers which are arranged uniformly and incontact between the layer of the multilayered element and thetransparent element, it is additionally possible to achievehomogenization of the lateral temperature distribution.

In a special configuration, the transparent element and/or the spacerhas a material which is selected from the group comprising glass and/orglass ceramic. Glass ceramic has various advantages:

It can be used for heat treatment in a wide temperature range from, forexample, 0° C. to, for example, 700° C. Glass ceramic has, for example,a softening point which lies above the temperature range.

It has a very low coefficient of thermal expansion. It is resistant tothermal shocks and is free of distortion in the abovementionedtemperature range of heat treatment.

It is chemically inert with respect to a large number of chemicals andhas low permeability for these chemicals. A chemical of this type is,for example, the process gas to which a layer or the entire multilayeredelement is exposed during the heat treatment.

It is optically partially transmissive in the spectral range of manyenergy sources for electromagnetic radiation, in particular in awavelength range in which a radiation density of the energy sources ishigh. A radiation source of this type is, for example, a halogen lampwith a high radiation density of between 0.1 and 4.5 μm.

Glass, in particular quartz glass, are likewise conceivable as amaterial for the transparent element. The advantage of glass is that itcan be used at high temperatures of up to 1200° C. These materialsexhibit a high transmission and low absorption in the spectral range ofan energy source in the form of a halogen lamp. The light passes throughthe transparent element substantially unhindered and reaches a layerwith a corresponding absorption for the electromagnetic radiation, thelayer taking up an amount of energy and being heated. The transparentelement is scarcely heated by the radiation.

In one process application it is possible for material of the heatedlayer to evaporate and be deposited on a relatively cold surface of thetransparent element. To prevent this, it is possible to ensure that thetransparent element is heated to a necessary temperature during the heattreatment. This is achieved by transmitting an amount of energy to thetransparent element by heat conduction and/or convection.Electromagnetic radiation which the transparent element absorbs is alsoconceivable. It is conceivable for the transparent element to have acoating which absorbs a certain part of the electromagnetic radiation.The energy taken up as a result can be passed on to the transparentelement made of glass or quartz glass. In this form, the transparentelement, comprising the glass element with the coating, is opticallypartially transmissive and can be used to transmit energy to themultilayered element both by heat radiation and by heat conduction.

In a special configuration, at least one layer of the multilayeredelement is in contact with a process gas. It is also conceivable for theentire multilayered element to be exposed to the process gas. An inertgas (molecular nitrogen or noble gas) comes into consideration forexample as the process gas. The process gas does not react with amaterial of the layer. However, a process gas which does react with amaterial of the layer is also conceivable. Under the action of theprocess gases, the functional layer forms. For example, the process gashas an oxidizing or reducing effect on a material of the layer. Possibleprocess gases for this are oxygen, chlorine, hydrogen, elementalselenium, sulfur or a hydride. It may also be an etching process gasessuch as HCL or the like. Further examples of the process gas are H₂S andH₂Se, which are used in the production of a thin-film solar cell (seebelow). Finally, all gases or gas mixtures which react with a materialof a layer in a corresponding way are conceivable. It is advantageous ifthe layer is exposed to a defined process-gas atmosphere. The definedprocess-gas atmosphere comprises, for example, a partial pressure of theprocess gas or gases during the heat treatment. It is also conceivable,for example, for a layer or the multilayered element to be in contactwith a vacuum for heat treatment.

A defined process,-gas atmosphere can be achieved, for example, bydirecting the process gas past the layer at a specific velocity. In thiscase, a process gas with various partial pressures can act on the layerin the course of the heat treatment. It is also conceivable for variousprocess gases to be successively in contact with the layer of thelayered element.

Preferably, at least the layer which is in contact with the process gasis enclosed. This is achieved, for example, by sheathing the layer, itbeing possible for the sheathing to be secured to the supporting layer.The sheathing is filled with the process gas before or during the heattreatment. The process gas is in this case concentrated on a surface ofthe layer of which the properties are to be influenced by the processgas.

In this way it is possible to prevent a surrounding area from beingcontaminated by the process gas. This is important in particular whenusing a corrosive and/or toxic process gas. Furthermore, it is possibleto operate with a stoichiometric amount of process gas necessary forconversion of the layer. There is no unnecessary consumption of processgas.

In a special configuration of the invention, the multilayered element isarranged in a heat-treatment container. In this case, at least onecontainer wall of the heat-treatment container has a transparentelement. The heat-treatment container has the advantage that itautomatically forms the sheathing of the layer or the entiremultilayered element. The sheathing does not need to be secured to themultilayered element. In the case of a closable heat-treatmentcontainer, the process-gas atmosphere can be set in a specificallyselective and easy way. For example, the heat-treatment container offersa sufficiently large volume for the process gas required during the heattreatment. If the heat treatment requires a homogeneous and reproducibledistribution of the process gas over a layer, a gas discharge from theheat-treatment container can also be set in a specifically selectiveway. This may be necessary, for example, whenever the heat treatment iscarried out at a very high heating-up rate. In this case, the processgas expands. If the heat-treatment container does not withstand the gaspressure thereby occurring, the heat-treatment container is deformed oreven destroyed. However, deformation should be prevented, for example,if the multilayered element rests on the base of the heat-treatmentcontainer. Deformation of the heat-treatment container may lead to alateral temperature inhomogeneity in the multilayered element.

Moreover, the heat-treatment container may be a means for transportingthe multilayered element during heat treatment. The heat-treatmentcontainer has the advantage that it is not possible, for example, torule out the possibility of a layer (supporting layer or substrate) ofglass breaking during the heat treatment. In the event of such asubstrate breaking, the broken material can be easily removed from theheat-treatment units or from the apparatus for heat treatment. Thiscontributes to stabilizing the heat-treatment process.

In a particular configuration, the container wall of the heat-treatmentcontainer which has the transparent element is a cover and/or a base ofthe heat-treatment container. For example, one layer of the multilayeredelement rests directly on the transparent element of the base. Asdescribed above, the transparent element may have spacers. The coverlikewise has the transparent element, which, for example, is not incontact with the multilayered element or a layer of the multilayeredelement. In this way, the layer of the multilayered element which restson the base can be heated by heat conduction, the layer facing the covercan be heated by heat radiation. The layer facing the cover can easilybe exposed to a process gas.

In a further configuration, the base and/or the cover of theheat-treatment container is formed by in each case at least onemultilayered element. In this case, the layer of the multilayeredelement which, for example, is intended to come into contact with aprocess gas is directed into the interior space of the heat-treatmentcontainer. This solution is possible if the multilayered element or thelayers of the multilayered element have a low coefficient of thermalexpansion and/or the heat-treatment rate is low. For a highheat-treatment rate, the multilayered element advantageously has asupporting layer with a high coefficient of thermal conductivity. Thesupporting layer is directed outward. For example, here the supportinglayer is a transparent element as described above.

In a special configuration, the heat-treatment container, thetransparent element and/or the energy transmitter have a material whichis inert with respect to a process gas. Moreover, it is advantageous foran entire heat-treatment process area to be inert with respect to theprocess gas used. The process area also includes, for example, theenergy source (primary energy source).

The material is selected according to the process gas. Glass, glassceramic and ceramic are conceivable, for example. A fiber-reinforcedmaterial, such as carbon-fiber-reinforced graphite can similarly beused. A material such as SiC, which has a high coefficient of thermalconductivity, is also conceivable. The heat-treatment container mayconsist of a metal or an alloy. A plastic which is resistant up to aspecific temperature is similarly possible.

In addition to being chemically inert with respect to the process gas,the following properties are of advantage for the material of theheat-treatment container:

The material of the heat-treatment container is free from distortionunder the heat-treatment conditions. It is also resistant to temperatureshocks. This is the case in particular whenever it has a low coefficientof thermal expansion.

The thermal softening point of the material of the heat-treatmentcontainer lies above a maximum temperature of the heat treatment.

The heat-treatment container exhibits a low or defined permeability withrespect to a process gas.

In a special configuration, there is a device for detecting a dimensionof at least one physical parameter of the apparatus and/or aheat-treatment unit that is dependent on the heat treatment, forcontrolling the first and second partial amounts of the amount ofenergy.

One conceivable parameter is an absorption, transmission and/orreflection property of a layer. The dimension of the parameter is thevalue of the parameter. For example, a wavelength of a maximumabsorption may depend on the temperature. The dimension of the parameterwould in this case be the corresponding wavelength.

In particular, the parameter is a temperature of the multilayeredelement. In this case, the dimension is a value of the temperature. Thedetection of the temperature of a layer of the multilayered element, ofthe transparent element and/or of the heat-treatment container or a wallof the heat-treatment container is also conceivable. During the heattreatment, it is always possible for at least one parameter of themultilayered element and/or of a layer to be detected. For example, thepartial amount of the amount of energy which is taken up by the layer isincreased or decreased on the basis of the detected temperature of alayer. In this way, a temperature inhomogeneity or a temperaturegradient in the direction of the thickness of the multilayered elementcan be avoided. This temperature inhomogeneity can, however, also beincreased, should this be necessary.

For example, the device for detecting the temperature is be a pyrometer,which is directed at the layer. The pyrometer detects, for example, theheat radiation which is emitted by the layer. The temperature of thelayer can be concluded on the basis of the heat radiation. A temperaturedetector which is connected to the layer and the temperature of which iscontrolled by heat conduction is also conceivable.

It is also conceivable for the temperature of the layer or of themultilayered element not to be measured directly but indirectly. Forexample, a pyrometer is directed at the heat-treatment container inwhich the multilayered element is heat-treated. The temperature of theheat-treatment container may be influenced by the temperature of themultilayered element. The temperature of the layer of the multilayeredelement is concluded on the basis of the temperature of theheat-treatment container. The amount of energy or the partial amount ofthe amount of energy is controlled on the basis of the measuredtemperature of the heat-treatment container. For this purpose, forexample, a kind of “calibration measurement” is to be carried out priorto the heat treatment, representing a relationship between the measuredtemperature of the heat-treatment container and the actual temperatureof the layer or of the layered element. The “calibration measurement”indicates a desired value of the temperature. The actual value isdetected. A comparison between the desired value and the actual valuesupplies a controlled variable for controlling the amounts of energy.The detection (and also the control of the partial amounts of the amountof energy) takes place in particular with a local resolution in thedirection of the thickness of the multilayered element and with atemporal resolution within the time frame of the heat treatment. Forexample, the multilayered element is heated up at a heat-treating rateof 25° C./s. In that case, both the detection and the control of thepartial amounts of the amount of energy would take place so quickly thata temperature difference between the layers of the multilayered elementduring the heat treatment remains below a prescribed maximum, forexample.

The temperature inhomogeneity in the direction of the thickness may, incombination with a transient deformation of the multilayered element,also lead to a lateral temperature inhomogeneity in the multilayeredelement. Lateral means, for example, within a layer of the multilayeredelement perpendicular to the direction of the thickness. For example,the multilayered element rests on a base of graphite. The supply ortake-up of the amount of energy by the layer of the multilayered elementresting on the base takes place through heat conduction. A temperatureinhomogeneity in the direction of the thickness may cause a transientdeformation of the multilayered element in the form of bending of themultilayered element. In this case, the contact between the multilayeredelement and the base of the heat-treatment container that is necessaryfor the heat conduction is partially detached. As a consequence of this,there is a lateral temperature inhomogeneity of the resting layer or ofthe multilayered element. It is therefore particularly advantageous if,for the detection of the parameter (and control of the amounts ofenergy), there is a local resolution not only in the direction of thethickness but also laterally.

In a special configuration, the parameter is a deformation of themultilayered element. The occurrence of a temperature inhomogeneity maycause deformation. For example, the multilayered element is concavelycurved. The multilayered element rests on the base of, for example, aheat-treatment container. Concave deformation has the effect that adistance between the resting surface and the multilayered element formsin the edge region of the multilayered element. A laser interferometryor laser light reflection device can be used, for example, to detect adimension of such a deformation. The control of the amounts of energytakes place on the basis of the dimension. It is advantageous if thedimension is detected in an early stage of the deformation and it ispossible to react quickly to it.

For an abovementioned device for detecting a dimension of a parameterwhich is dependent on the heat treatment with the aid of an opticaldevice (for example a laser), it is advantageous if the layer which isto be examined is accessible for light from the optical device and adetection signal can be unequivocally assigned to the parameter to bedetected. The wavelength of a laser should, for example, differsufficiently from the heat radiation of the multilayered element. If theapparatus is equipped with a heat-treatment container, it would beadvantageous if the transparent element is sufficiently transparent tothe light of the laser.

With the aid of the apparatus, it is also possible to achieve a desireddeformation of the multilayered element. For this purpose, it may alsobe appropriate to monitor the deformation during the heat treatment inthe manner described above. For example, it is possible to produce acurved thin-film solar cell. To achieve specifically selectivedeformation, the multilayered element is, for example, laid on acorresponding mold or mask. The mold or mask may directly be an energysource. The multilayered element is heated to above a softening point ofthe supporting layer. As a consequence of this, the multilayered elementadopts a shape which corresponds to that of the mask or mold. The maskis, for example, integrated in a base of the heat-treatment container.The mask could be, for example, the transparent element. To achieve theobject, in addition to the apparatus there is specified a method forheat-treating a material being processed under a specific process-gasatmosphere of a process gas, with the aid with the method steps: a)arranging the material being processed in the heat-treatment space ofthe heat-treatment container and b) heat-treating the material beingprocessed while establishing the pressure gradient of the further gasatmosphere in the intermediate space between the heat-treatmentcontainer and the heat-treatment chamber.

The intermediate space with the further gas, for example a purging gas,acts as a buffer, so that the process gas which is located in theheat-treatment space cannot reach the heat-treatment chamber, or only ina rarefied form. Contamination or corrosion of the heat-treatmentchamber can be prevented. The selection of the material of theheat-treatment chamber is virtually independent of the process gas. Theintermediate space can be filled once with the purging gas. It is alsoconceivable for a continuous stream of purging gas to be passed throughthe intermediate space, removing from the intermediate space process gaspossibly escaping from the heat-treatment container. The stream ofpurging gas is produced by the pressure gradient. A removal of escapingprocess gas is also achieved by a pressure gradient being establishedfrom the heat-treatment space of the heat-treatment container to theintermediate space.

In a special configuration, a gas pressure of the heat-treatment spaceand/or a gas pressure of the intermediate space and/or a gas pressure ofthe buffer space is set. In particular, a gas pressure of theheat-treatment space which is less than the gas pressure of theintermediate space is chosen for establishing the pressure gradient. Inaddition, it is also conceivable in particular for a gas pressure of thebuffer space that is less than the gas pressure of the heat-treatmentspace and/or less than the gas pressure of the intermediate space to bechosen. In this way, a pressure gradient can be set between theheat-treatment space and the intermediate space. This is achieved inparticular by the heat-treatment chamber being arranged in a shroud.

In a further configuration, the heat treatment comprises at least oneheating-up and/or at least one cooling-down process. In this case, it ispossible in particular to run through a plurality of heating-up andcooling-down phases.

According to a further configuration, a multilayered element with alayer and at least one further layer is used as the material beingprocessed.

In this case, a multilayered element with a layer which has copper,indium, gallium and/or selenium is used in particular. A supportinglayer of the multilayered element is made in particular of glass and/ormetal.

In a special configuration, a process gas which is selected from thegroup comprising H₂S, H₂Se, H₂, He and/or N₂ is selected.

In particular, a further gas, which is selected from the groupcomprising N₂ and/or noble gas, is used.

The method is suitable in particular for producing a photovoltaicthin-film chalcopyrite absorber of a solar cell and/or of a solarmodule.

The process-gas atmosphere and the further gas atmosphere may beproduced before, during or after the heat treatment. The materials beingprocessed can in this case be brought simultaneously into contact with aplurality of process gases (gas mixture). It is also conceivable for thematerial being processed to be brought successively into contact withdifferent process gases and/or purging gases. Consequently, a variableprocess gas profile (temporal sequence of different partial pressures ofthe process gas or gases) is possible. In this way, it is possible, forexample, to use both oxidizing and reducing process gases, or tointroduce a dopant into the material being processed in a specificallyselective way.

In a special configuration, there is a shroud of the heat-treatmentcontainer, so that there is a buffer space for gas between theintermediate space and the heat-treatment space.

In the intermediate space between the heat-treatment chamber and theheat-treatment container, a gas pressure of a purging gas that isgreater than the gas pressure in the buffer space is produced. For thispurpose, gas outlet openings are preferably provided in the shroud, ledto the outside for example via a manifold pipeline through theintermediate space and through the heat-treatment chamber, and directedthere for example into a gas disposal unit. Consequently, the pressureprevailing in the buffer space of the shroud is approximately the sameas that in the gas disposal unit (for example atmospheric pressure). Theeffect of this arrangement can be referred to as gap counterflowpurging, which serves the purpose of opposing the stream of process gasdiffusing out of the heat-treatment space with a counteracting stream ofinert gas at a gap of a lead-through in the shroud, for example at anassembly gap of a component of the shroud, with the aim of preventingcondensation of process gases on the walls of the heat-treatment chamberor corrosion of the walls of the heat-treatment chamber. The latter canalso be achieved, moreover, by suitable coating of the walls of theheat-treatment chamber.

The gap counterflow purging works on the following principle: theheat-treatment container filled with the process gas is arranged in theshroud. It is not possible to rule out the possibility of the processgas getting into the buffer space of the shroud.

The buffer space of the shroud and the intermediate space between theheat-treatment container and the heat-treatment chamber are connected bygaps or openings. A pressure gradient from the intermediate space to thebuffer space is built up as a result of the choice of the gas pressures.This is achieved, for example, by extracting the purging gas from thebuffer space by suction and/or introducing the purging gas into theintermediate space and a resultant pressure build-up with respect to thepressure of the buffer space, which may, as described above, be incontact with the surrounding area of the heat-treatment apparatus. Thisproduces a stream of purging gas from the intermediate space to thebuffer space. The process gas does not reach the chamber wall of theheat-treatment chamber. In this way, a temperature of the heat-treatmentchamber, the gas pressure of the buffer space and/or the gas pressure ofthe intermediate space are set in particular during the heat treatment.

In a special configuration, a multilayered element with a layer and atleast one further layer is used as the material being processed and/orfurther material being processed.

In this case, the heat treatment takes place by an amount of energybeing taken up by the multilayered element, with a first partial amountof the amount of energy being taken up by the first layer and a secondpartial amount of the amount of energy being taken up by the secondlayer, with at least one energy source being used for supplying theamount of energy to the multilayered element. In this case, an apparatusdescribed above is used in particular. The method steps are: arrangingthe multilayered element between a first and at least one second energysource, so that the first layer is arranged between the first energysource and the second layer and the second layer is arranged between thesecond energy source and the first layer, with at least one energysource of a specific electromagnetic radiation with a radiation fieldbeing used as the energy source, and at least one of the layersabsorbing the electromagnetic radiation and being arranged in theradiation field of the energy source, and arranging a transparentelement in the radiation field of the energy source between the energysource and the layer which lies in the radiation field of the energysource and absorbs the specific electromagnetic radiation, and heattreatment of the multilayered element.

In a special configuration, the transparent element absorbs a specificamount of energy and supplies the amount of energy to the layer. In afurther configuration, detecting a dimension of a physical parameter ofthe multilayered element that is dependent on the heat treatment iscarried out for controlling the take-up of the amount of energy duringthe heat treatment and controlling the first and second partial amountsof the amount of energy. In a special configuration, the transparentelement supplies the layer with the amount of energy by heat conductionand/or heat radiation.

In a special configuration, a multilayered element with a layer whichhas copper, indium, gallium and/or selenium is used. In particular, amultilayered element with a supporting layer made of glass and/or metalis used. The supporting layer may, for its part, have a coating (forexample a metal layer on a glass plate). A gas which is selected fromthe group comprising H₂S, H₂Se, H₂, He and N₂ is used as the processgas. The method serves in particular for producing a photovoltaicthin-film chalcopyrite absorber of a solar cell and/or of a solarmodule. In the case of the solar module, there are a multiplicity ofindividual solar cells connected in series. The glass is preferablysoda-lime glass. The corresponding layer acts as a supporting layer. Onthe supporting layer, a molybdenum layer is applied as an electrode and,over the molybdenum layer, a functional layer is applied, that is acopper-indium-gallium-sulfoselenide (CIGSSe) semiconductor layer. Athickness of the layered element, comprising the glass element andsemiconductor layer, is typically 2 to 4 mm, with a molybdenum layer ofapproximately 0.5 μm and a semiconductor layer of approximately 3 μm.The specified range for the thickness of the multilayered element is notto be used exclusively. A limiting factor is a capability for producinga large substrate which is as planar as possible, and consequently canbe processed with the described apparatus or with the described methodto form a multilayered element. To sum up, the following advantages areobtained with the invention:

A material being processed can be heat-treated in any desiredprocess-gas atmosphere. In particular, a toxic and/or corrosive processgas can be used. Condensations of a process substance on the chamberwalls can be avoided.

A heating-up and cooling-down profile can be variably set up.

A material being processed in the form of a multilayered element of alarge surface area with an unsymmetrical layer structure (for example amultilayered element with a single layer on a supporting layer) can beheat-treated at a high heat-treating rate of over 1° C./s.

The layers of the multilayered element may in this case have a greatlydiffering coefficient of thermal conductivity and/or greatly differingemissivity.

A temporal and local resolution of the detection and the control of adimension of a parameter dependent on the heat treatment allows heattreatment to be conducted particularly safely. For example, it ispossible to react to a change in a property of the material beingprocessed (for example emissivity or absorptivity) during the heattreatment and set the process parameters (pressure, temperature, energydensity, etc.) to it.

Heat treatment to near a softening point of a supporting layer of thematerial being processed is possible.

In the case of heat treatment beyond the softening point of thesupporting layer, a permanent deformation of the multilayered element ispossible.

A defined heat-treatment area with a defined process-gas atmosphere canbe created. Various process gases with various partial pressure profilescan be set simultaneously or successively before, during and/or afterthe processing.

All the method steps necessary for the processing can be carried outwith a single apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

An apparatus for heat-treating a material being processed and acorresponding method for this are represented on the basis of severalexemplary embodiments and the associated figures. The figures areschematic and do not represent illustrations that are true to scale.

FIG. 1 shows a cross section from the side of an apparatus forheat-treating at least one material being processed.

FIG. 2 shows a method of heat-treating at least one material beingprocessed.

FIG. 3 shows a detail of a cross section from the side of an apparatusfor heat-treating at least one material being processed.

FIG. 4 shows a cross section from the side of an apparatus forheat-treating at least one material being processed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The starting point is an apparatus 1 for heat-treating a material beingprocessed 3 (FIGS. 1 and 4) under the process-gas atmosphere 111 of aprocess gas 4. The apparatus 1 has a heat-treatment unit 6 with aheat-treatment container 11, a shroud 12 of the heat-treatment container11, a heat-treatment chamber 13 and an energy source 5 for the take-upof an amount of energy by the material being processed 3. Theheat-treatment container 11 is filled with the process gas 4 viaprocess-gas inlet and outlet openings 113 (FIG. 3). The heat-treatmentcontainer 11 lies in a shroud 12, so that there is a buffer space 15between the shroud 12 and the heat-treatment container 11. Together withthe shroud 12, the heat-treatment container is arranged in an evacuableheat-treatment chamber 13, so that there is a distance 18 between theheat-treatment container 11 and the heat-treatment chamber 13. Forproducing the further gas atmosphere 141 of the intermediate space,there is a closable opening 19 in the heat-treatment chamber 13. Afurther gas opening is provided in the shroud 12 and is led to theoutside by the pipe connection 19 a through the heat-treatment chamber13 to the surrounding area 7.

The material being processed 3 is arranged in the heat-treatmentcontainer 11 in the method step 21 (FIG. 2). After that, the heattreatment (method step 23) takes place, with the pressure gradient 2being established between the buffer space 15 of the shroud 12 and theintermediate space 14.

In a further embodiment, the pressure gradient 2 is set (method step 22)and, subsequently, the heat treatment 23 is carried out. In this case, acheck is kept on the change in the pressure gradient during the heattreatment 23.

FIG. 3 illustrates the principle of gap counterflow purging. The arrowsindicate a pressure gradient 2 and a resultant gas stream. During theheat treatment 23, a process-gas atmosphere 111 with the gas pressure112 of the heat-treatment space 16 prevails in the heat-treatment space16 of the heat-treatment container 11. The process gas 4 can escape intothe buffer space 15 of the heat-treatment unit 6 through a gap 8 of theheat-treatment container 11. To prevent the heat-treatment chamber 13being contaminated by the process gas 4, the buffer space 15 isconnected to a surrounding area 7 in such a way that the gas pressure152 (gas atmosphere 151) of the buffer space 15 corresponds to a gaspressure of the surrounding area 7. The gas pressure of the surroundingarea 7, and consequently the gas pressure 152 of the buffer space 15, isless than the gas pressure 112 of the heat-treatment space 16 and lessthan the gas pressure 142 of the intermediate space 14.

At the same time, it is ensured that a gas pressure 142 whichapproximately corresponds to the gas pressure 112 of the heat-treatmentspace 16 of the heat-treatment container 11 prevails in the intermediatespace 14 between the heat-treatment chamber 13 and the heat-treatmentcontainer 11. It is slightly greater, so that the process gas 4 does notpass through a gap 9 of the shroud 12 into the intermediate space 14. Asa result of the fact that the smaller gas pressure 152, in comparisonwith the gas pressures 112 and 142, prevails in the surrounding area 7,process gas 4 possibly escaping into the buffer space 15 of the shroud12 is transported in the direction of the surrounding area 7 on thebasis of the prevailing pressure gradient 2.

The embodiment according to FIG. 3 is equipped with additional infraredreflectors 51 and tungsten-halogen bar heating lamps 5, which areinserted in quartz jackets 52. The quartz jackets 52 are led through thevaccuum wall of the heat-treatment chamber 13 and sealed from theatmosphere by vacuum seals 53.

What is claimed is:
 1. An apparatus for heat-treating at least onematerial being processed under a specific process-gas atmosphere of atleast one process gas with the aid of a heat-treatment unit, comprising:a heat-treatment chamber; a shroud arranged in the heat-treatmentchamber so as to define an intermediate space and a buffer space; aheat-treatment container arranged in the buffer space, saidheat-treatment container defining a heat-treatment space for keeping thematerial being processed under the process-gas atmosphere during theheat treatment; at least one energy source for making the material beingprocessed take up an amount of energy; and means for producing in theintermediate space a further gas atmosphere of a further gas, differentfrom the process-gas atmosphere, wherein the heat-treatment space, thebuffer space and the intermediate space are connected with each other bygaps in such a way that a pressure gradient can be set between theheat-treatment space and the intermediate space.
 2. A method forheat-treating a material being processed under a specific process-gasatmosphere of a process gas, with the aid of a heat-treatment apparatusthat has a heat-treatment chamber provided with a shroud that defines anintermediate space between the heat-treatment chamber and the shroud,the method comprising the steps of: arranging the material beingprocessed in a heat-treatment space of a heat-treatment container;arranging the heat-treatment container in the heat-treatment chambersuch that there is a buffer space between the heat-treatment containerand the shroud; and heat-treating the material being processed whileestablishing a pressure gradient between the heat-treatment space andthe intermediate space.
 3. The method as claimed in claim 2, in whichestablishing the pressure gradient comprises selecting the pressures inthe heat-treatment space, the buffer space and the intermediate spacesuch that the gas pressure in the intermediate space is slightly greaterthan the gas pressure in the heat-treatment container, and that the gaspressure in the buffer space is smaller than the gas pressure in theheat-treatment space and smaller than the gas pressure in theintermediate space.
 4. The method as claimed in claim 2, in which amultilayered element with a layer and at least one further layer is thematerial being processed.
 5. The method as claimed in claim 4, whereinthe multilaylered element has a layer with at least one of copper,indium, gallium and selenium.
 6. The method as claimed in claim 4,wherein the multilayered element has a supporting layer made of glassand/or metal.
 7. The method as claimed in claim 2, wherein the processgas is selected from the group comprising H₂S, H₂Se, H₂, He and N₂. 8.The method as claimed in claim 2, wherein a further gas which isselected from the group comprising N₂ and/or noble gas is used.
 9. Themethod as claimed in claim 2 for producing a photovoltaic thin-filmchalcopyrite absorber of a solar cell and/or a solar module.
 10. Themethod as claimed in claim 5, wherein the multilayered element has asupporting layer made of glass and/or metal.
 11. The method as claimedin claim 3, wherein the process gas is selected from the groupcomprising H₂S, H₂Se, H₂, He and N₂.
 12. The method as claimed in claim3, wherein a further gas which is selected from the group comprising N₂and/or noble gas is used.
 13. The method as claimed in claim 3 forproducing a photovoltaic thin-film chalcopyrite absorber of a solar celland/or a solar module.